Manufacture of n-2-arylthiazole sulfenamide

ABSTRACT

N-aryl-thiazolesulfenamide is prepared by oxidative condensation by reacting a mercaptothiazole and an aryl amine in alcohol solvent and alkali metal hypochlorite at a temperature below 0* C. The preferred N-aryl-2-benzothiazole sulfenamide is used to offset the decrease in scorch encountered upon incorporating a phenylenediamine antiozonant in the rubber formulation.

United States Patent Shoffner 1 June 27, 1972 s41 MANUFACTURE OF N-2-3,161,648 12/1964 Rodgers et a] ..260/306.6

ARYLTHIAZOLE SULFENAMIDE OTHER PUBLICATIONS [72] inventor: James P.Shoifner, Elk Grove Village, 111.-

[73] Assignee: Universal Oil Products Company, Des

Plaines, Ill.

[22] Filed: Aug. 22, 1969 [21] Appl. N0.: 852,474

[52] US. Cl ..260/06.6 A, 260/833, 260/302 S [51] Int. Cl. ..C07d 91/44[58] Field of Search ..260/306.6 A, 302 S [56] References Cited UNITEDSTATES PATENTS 2,581,921 1/1952 Alliger ..260/306.6

Carr et al., J. Org. Chem., 14, 921- 34 (1949).

Primary Examiner-Alex Mazel Assistant Examiner-R. J. GallagherAttorney-James R. Hoatson, Jr. and Bernard L. Kramer [57] ABSTRACTN-aryl-thiazolesulfenamide is prepared by oxidative condensation byreacting a mercaptothiazole and an aryl amine in alcohol solvent andalkali metal hypochlorite at a temperature below 0 C. The preferredN-aryl-Z-benzothiazole sulfenamide is used to offset the decrease inscorch encountered upon incorporating a phenylenediamine antiozonant inthe rubber formulation.

10 Claims, No Drawings MANUFACTURE OF N-2-ARYLTI-IIAZOLE SULFENAMIDEBACKGROUND OF THE INVENTION Various benzothiazolesulfenarnides arepresently used as accelerators in the vulcanization of rubber. Thesulfenarnides being so used are the cycloalkyl, the alkyl or theoxyalkylene derivatives.

Numerous methods are disclosed in the prior art for the preparation ofthe sulfenamides set forth above. One method is referred to as oxidativecondensation and utilizes chlorine, sodium hypochlorite, iodine,hydrogen peroxide, etc. as the oxidizing agent. The temperature used inthese preparations is above C. and may range from 5 to 30 C. or more.Another method involves the reaction between benzothiazole sulfurchloride with a primary aliphatic amine. Still another method involvesthe reaction of metallic thiazoyl mercaptides with N- chloro derivativesof secondary amines. Still another method involves the reaction of athiazolyl disulfide with an amine. These methods work satisfactorily invarying degrees for the preparation of the specific derivativeshereinbefore set forth by apparently the oxidative condensation processappears to be the preferred method.

Although extensive research has been conducted in connection with themanufacture of various benzothiazolesulfenamides, the prior art ispractically silent as to the preparation of the N-aryl-sulfenamidederivatives by the oxidative condensation process. Apparently thissilence is due to the fact that the N-aryl derivatives are not preparedby following the conventional oxidative condensation method. Thisinability to prepare the N-aryl derivatives by the oxidativecondensation process is mentioned in the article 'Ihiazolesulfenamidesby Carr, Smith and Alliger which appeared in J. Organic Chemistry, 14,921-34 (1949).

The present invention is based on the discovery thatN-arylbenzothiazolesulfenamides can be prepared by the oxidativecondensation process provided that certain critical modifications arepracticed. These critical modifications include the use of an alkalimetal hypochlorite, an alcohol solvent and a temperature of below 0 C.In the absence of these critical requirements, the desiredN-aryl-benzothiazolesulfenamide is not produced.

As hereinbefore set forth, the use of an alkali metal hypochlorite iscritical. Sodium hypochlorite is preferred. Other alkali metalhypochlorites and particularly potassium hypochlorite may be used butnot necessarily with equivalent results. The use of the alkali metalhypochlorite is critical because other conventional oxidizing agents,such as potassium iodide, iodine, hydrogen peroxide, etc., wereunsuitable in the preparation of the desired product.

Also, as hereinbefore set forth, the reaction is effected in thepresence of an alcohol solvent. Methanol is particularly preferred.Other alcohol solvents include ethanol, propanol, butanol, etc.

Also, as hereinbefore set forth, the reaction temperature must be below0 C. and thus may range from 20 to 0 C. and preferably is within therange of l0 to 0 C., although even lower temperatures may be used ifadvantages appear therefor. However, the reaction proceedssatisfactorily at a temperature of -l0 to -5 C. so that generally therewill be no necessity to utilize lower temperatures.

In a preferred embodiment, mercaptobenzothiazole is utilized as areactant. However, it is understood that other thiazoles may be used as,for example, 2-mercapto-4,5 dimethylthiazole,2-mercapto-4-ethylthiazole, 2-mercaptonaphthothiazole,2-mercapto-4-phenylbenzothiazole, 2-mercapto-methylbenzothiazole, etc.,but not necessarily with equivalent results.

Any suitable aromatic amine is used as a reactant. The differentaromatic amines may impart different properties to the final product andthus the particular aryl amine will be selected with reference to theultimate use of the sulfenamide.

' conventional proportions, which may range from 0.5 to 3 andIllustrative aromatic amines include aniline, p-methylaniline,p-methoxyaniline, p-chloroaniline, etc. Other substituted anilinesinclude o, m and p-alkylanilines in which the alkyl contains from one tosix carbon atoms and 2,3-, 2,4-, 2,5-, 2,6- 3,4- or 3,5- dialkylaniline,each alkyl containing one to six carbon atoms. Corresponding naphthylamines may be used to prepare the N-naphthyl derivatives.

The oxidative condensation may be effected in any suitable manner withthe critical modifications hereinbefore set forth. In a preferred methodthe alkali metal thiazole and particularly sodium mercaptobenzothiazoleis prepared first and then is reacted with the aryl amine under thecritical conditions herein set forth. The thiazole and aryl amine arereacted in equal mole proportions but generally an excess of the arylamine is used and may range up to 5-mole proportions thereof per moleproportion of the thiazole. The alkali metal hydroxide is used initiallyto form the alkali metal mercaptobenzothiazole and will be used in atleast equal mole proportions but a slight excess up to 10 percent may beemployed. In a particularly preferred method, mercaptobenzothiazole,aryl amine and sodium hydroxide are dissolved in the alcohol solvent,and the solution is cooled to a temperature of below 0 C. Any suitablemethod of cooling may be used and, in one method, comprises anice-alcohol bath. Commercial Formula 30, comprising a mixture ofmethanol and ethanol, may be used with ice as the cooling medium. Thecooled solution then is slowly added to an aqueous solution of alkalimetal hypochlorite and preferably of sodium hypochlorite whichpreviously had been chilled to a temperature of below 0 C. The alkalimetal hypochlorite is used in sufficient concentration and may rangefrom equal molar and preferably an excess up to 25 molar percent of thethiazole is used. As mentioned above the sodium hypochlorite preferablyis prepared as a solution in cold water and may comprise from 5 to 40percent and preferably from 5 to 15 percent by weight of thehypochlorite.

The commingling of the reactants is accompanied by stirring, after whichthe mixture preferably is stirred for an additional time to complete thereaction. The additional stirring will be continued for the desired timewhich may range from 15 minutes to 1 hour or more. After completion ofthe reaction, the reaction mixture is filtered and the sulfenamideproduct is recovered as a solid product. The solid product may be usedas such or, when desired, it may be purified inany conventional manner.

As hereinbefore set forth, the N-aryl-benzothiazolesulfenamide is usedto offset the decrease in scorch time encountered when aphenylenediarnine antiozonant is incorporated in the rubber formulation.However, as hereinbefore set forth, the difierent substituted arylderivatives possess different specific properties and thus theparticular derivative to be used will be selected with reference to theparticular rubber properties desired. In some cases the elongationproperties are of more importance than the other properties as, forexample, the tensile strength. The specific properties appear to berelated to the basicity of the amine.

The sulfenamide will be used in the rubber formulation in preferablyfrom 1 to 2 parts of the sulfenamide per parts of the rubber hydrocarbonin the formulation. The sulfenamide of the present invention isincorporated in the rubber fonnulation in any suitable manner andconveniently is incorporated during milling of the various ingredientsinto the rubber hydrocarbon. The various ingredients include in additionto the sulfenarnides of the present invention, carbon, zinc oxide,sulfur, stearic acid, antioxidant, antiozonant, etc., all of these beingused in conventional concentrations. Following the mixing, the mixtureis subjected to vulcanization in conventional manner.

The following examples are introduced to illustrate further the noveltyand utility of the present invention but not with the intention ofunduly limiting the same.

EXAMPLE I The sulfenamide of this example is the N-phenylsulfenamide ofmercaptobenzothiazole. It was prepared by forming a solution in methanolof 34 g. (0.2 mole) of mercaptobenzothiazole, 46.5 g. (0.5 mole) ofaniline and 20 ml. of a 50 aqueous solution of sodium hydroxide andcooling the solution to 8 C. in an ice-alcohol bath. The alcohol usedwas commercial Formula 30. A separate solution (150 ml.) of commercial10 percent by weight of sodium hypochlorite was chilled to 8 C. Thesecond solution was added dropwise over a period of minutes into thefirst solution, with continuous stirring. The mixture was stirredfor anadditional minutes and then filtered. There was recovered 10.5 g. ofsolid material comprising the desired sulfenamide. The sulfenarnide waspurified by elution from a column of alumina (75 g. of 60-200 mesh) withether (1.5 liter) to yield N-phenylbenzothiazolesulfenamide, having amelting point if 126 129 C. The composition of the product was confirmedby NMR (nuclear magnetic resonance) and IR (infrared) analyses.

EXAMPLE II Np-methylphenylbenzothiazolesulfenarnide was prepared insubstantially the same manner as described in Example I. In thispreparation, 34 g. (0.2 mole) of mercaptobenzothiazole, 53.5 g. (0.5mole) p-methylaniline and 20 ml. of a 50 percent solution of sodiumhydroxide were dissolved in methanol (200 ml) and cooled to 8 C. in anice-Formula 30 alcohol bath. A separately prepared 10 percent solutionof sodium hypochlorite (150 ml) which previously had been chilled to 8C. was added dropwise to the first solution over a period of 20 minuteswhile being stirred and the stirring was continued for an addition 30minutes, after which the mixture was filtered. TheN-pmethylphenylbenzothiazolesulfenamide was recovered as a solid in anamount of 12 g. Here again the sulfenamide was purified by elution froma column of alumina with ether in the same manner as described inExample I. The product had a melting point of l44--l46 C. Thecomposition of the product was characterized by NMR and IR as describedin Example I.

EXAMPLE III The sulfenarnide ,of this example isN-p-methoxyphenylbenzothiazolesulfenamide and was prepared insubstantially the same manner as described in the previous examples. Inthis specific example, 34 g. (0.2 mole) of mercaptobenzothiazole, 62 g.(0.5 mole) of p-methoxyaniline and 20 m1. of 50 percent solution ofsodium hydroxide were dissolved in methanol and cooled to 8 C. in theice-alcohol bath. A 10 percent solution of sodium hypochlorite (150 ml)which previously had been chilled to 8 C. was added dropwise to thefirst solution over a period of 20 minutes with continuous stirring andfollowed by additional stirring for 30 minutes, after which the mixturewas filtered and the solid product purified and characterized in thesame manner as described in Example I. TheN-pmethoxyphenylbenzothiazolesulfenamide was recovered in a yield of 13g. and had a melting point of l l9 l 2 l C.

EXAMPLE IV Np-chlorophenyl-benzothiazolesulfenamide was prepared insubstantially the same manner as described in Example I except thatp-chloroaniline was charged in a concentration of 64 g. (0.5 mole). Thesolid product was purified by elution in the same manner as described inExample I.

EXAMPLE V As hereinbefore set forth, the use of the alkali metalhypochlorite is critical. This is illustrated in the present example inwhich a preparation similar to that described in Example I was attemptedusing potassium iodide instead of sodium hypochlorite. Under the samereaction conditions as described in Example I, thedesiredN-phenylbenzothiazolesulfenamide was not produced. Instead there wasproduced a very dark solution, probably resulting from considerableoxidation of the aniline and 2,2'-dithio-bis' benmthiazole.

EXAMPLE VI Still another run was made in a similar manner as describedin Example I except that hydrogen peroxide was used instead of sodiumhypochlorite. Here again the desired N-phenylbenzothiazolesulfenamidewas not produced. Instead there was produced only a clear solution whichcontained none of the desired product.

EXAMPLE VII As hereinbefore set forth it is essential that an alcoholsolvent be used in the preparation. Another preparation was attempted inthe same manner as described in Example I except that dimethyl formamidewas used instead of the methanol solvent. It was found that the dimethylformamide oxidized and the desired N-aryl-benzothiazolesulfenamide wasnot produced.

EXAMPLE VIII EXAMPLE IX As hereinbefore set forth, other methods wereinvestigated and found to be inoperative for the preparation of theN-arylbenzothiazolesulfenamide. The method attempted in this example wasthe reaction of 2 benzothiazole sulfenylchloride with aniline. In thereaction a solution of 2 benzothiazolesulfenychloride was prepared bytreating a solution of 2,2- dithio-bis-benzothiazole (33.2g. 0.1 mole)in methylene chloride (500 ml) with chlorine gas (7.] g). The sulfenylchloride so prepared was chilled to -8 C. and treated with a solution ofaniline (28 g., 0.3 mole) in methylene chloride ml). The precipitate wasfiltered and the solution concentrated. The major product of thisreaction was starting material and considerable decomposed materials.

When the reaction is run at ambient temperature without cooling, thereaction cannot be controlled and decomposition is even more severe.

EXAMPLE X N-phenyl-2-mercapto-4,5-dimethylthiazolesulfenarnide isprepared in substantially the same manner as described in the which alsohad been chilled to 5 C., is added dropwise over a period of 20 minutesinto the first solution, with continuous stirring. The mixture isstirred for an additional 45 minutes and then filtered. The solidmaterial is recovered as the desiredN-phenyl-4,5dimethyl-thiazolesulfenarnide.

EXAMPLE X] As hereinbefore set forth, theN-aryl-benzothiazolesulfenamide serves to offset the decrease in scorchtime encountered concentration of 1.25 phr (parts per 100 parts ofrubber hydrocarbon). For comparative purposes the results obtained whenusing N-cyclohexylbenzothiazole-2-sulfenarnide also are reported. Asmentioned above, N-cyclohexylbenzothiazole-2- sulfenamide is presentlyused on a large scale in commercial manufacture of rubber products.

The rubber formulation used in these runs was of the following recipe:

Ingredient Parts by Weight SBR I502 100 Furnace Black 40 Zinc Oxide 3Stearic Acid 2 Sulfur 2 Sulfenamide 1.25 Antiozonant (when used) 3.32

Mooney Scorch Benzothiazole 5 pt. pt. Run No.

Sulfenamide Antiozonanfi rise rise 1 N-cyclohexyl No 56.1 60.8 2N-cyclohexyl Yes 18.0 20.5 3 N-phenyl No 82.6 115.2 4 N-phenyl Yes 48.056.4 5 Np-methylphenyl No 80.4 105.6 6 N-p-methylphenyl Yes 43.7 49.8 7N-p-methoxyphenyl No 67.1 78.5 8 N-p-methoxyphenyl Yes 30.9 35.1

*N'-di-2-octyl-p-phenylenediamine As mentioned above, the sulfenamideswere used in a concentration of 1.25 phr. The antiozonant was used in aconcentration of 3.32 phr.

Referring to the data in the above table, it will be seen that thesulfenamides of the present invention offset the decrease in scorchencountered upon the addition of the antiozonant into the rubberformulation. For comparative purposes, it will be noted that thisdecrease in scorch time was considerably less than when usingN-cyclohexyl-benzothiazolesulfenamide.

EXAMPLE XII Also of importance is the proper curing of the rubberformulation in order to prepared a product of the desired physicalproperties. The specific physical properties desired will depend uponthe ultimate use of the rubber product. For example, the ultimateelongation is an important requirement.

In the preparation as described in Example XI, the sample containing thesame phenylenediamine antiozonant and N-cyclohexyl-benzotl'iiazolesulfenamide had an ultimate elongation of 550percent. The samples containing the same antiozonant and the N-phenyl,N-p-methylphenyl and N-p-methoxyphenyl derivatives had ultimateelongations of 445 percent, 520 percent and 575 percent,respectively.-Accordingly, for this requirement the N-p-methoxyderivative would be preferred.

EXAMPLE XIII When considering tensile strength of the rubber product asan important requirement, the N-p-methoxyphenyl derivative also appearsbest of the N-aryl derivatives. The sample containing the samephenylenediamine antiozonant and theN-pmethoxyphenyl-benzothiazolesulfenamide had a tensile strength of2,780 pounds. This is only slightly less than the tensile strength of3,000 pounds in the product containing the same phenylenediamineantiozonant and N-cyclohexylbenzothiazolesulfenamide.

I claim as my invention:

1. A process for preparing an N-aryl-thiazolesulfenamide by oxidativecondensation which comprises reacting a mercaptothiazole and an arylamine selected from the group consisting of aniline and alkyl, methoxyand chloro-substituted anilines in an alcohol of from one to four carbonatoms per molecule and an alkali metal hypochlorite at a temperaturebelow 0 C.

2. The process of claim 1 in which the thiazole is mercaptobenzothiazoleand the sulfenamide is N-arylbenzothiazolesulfenamide.

3. The process of claim 1 in which said aryl amine is aniline.

4. The process of claim 1 in which said alcohol is methanol.

5. The process of claim 1 in which said aryl amine is pmethylaniline.

6. The process of claim 1 in which said aryl amine is pmethoxyaniline.

7. The process of claim 1 in which said aryl amine is pchloroaniline.

8. The process of claim 2 in which said alkali metal hypochlorite issodium hypochlorite.

9. The process of claim 2 in which said temperature is from 20 to 0 C.

10. The process of claim 2 in which said temperature is from 1 0 to 0 C.

2. The process of claim 1 in which the thiazole is mercaptobenzothiazoleand the sulfenamide is N-aryl-benzothiazolesulfenamide.
 3. The processof claim 1 in which said aryl amine is aniline.
 4. The process of claim1 in which said alcohol is methanol.
 5. The process of claim 1 in whichsaid aryl amine is p-methylaniline.
 6. The process of claim 1 in whichsaid aryl amine is p-methoxyaniline.
 7. The process of claim 1 in whichsaid aryl amine is p-chloroaniline.
 8. The process of claim 2 in whichsaid alkali metal hypochlorite is sodium hypochlorite.
 9. The process ofclaim 2 in which said temperature is from -20* to 0* C.
 10. The processof claim 2 in which said temperature is from -10* to 0* C.